Die casting machines and processes are well known and in widespread use in the high volume manufacture of metal or alloy components. In general, a die casting machine comprises a fixed die member and a movable die member which define therebetween a die cavity in which an individual charge of molten metal is introduced and solidified to form a die casting. A vertically or horizontally oriented shot sleeve is connected to the fixed die member and includes an opening through which the charge of the molten metal to be cast is introduced ahead of a plunger disposed in the shot sleeve. When the molten metal charge is introduced into the shot sleeve, the plunger is advanced in the shot sleeve toward the die members in a manner to introduce the charge into the die cavity through a runner or gate communicating the die cavity and shot sleeve. After the metal solidifies in the die cavity, the movable die member is separated from the fixed die member to allow ejection of the die casting. The die members then are closed and another individual molten metal charge is introduced into the die cavity to make another die casting. This cycle is repeated to make additional die castings in high volume.
In a typical high volume die casting operation, the successive charges of molten metal are supplied to the shot sleeve from a heated melt transport ladle that receives an appropriate amount (charge) of molten metal from a melting furnace and then is moved to the shot sleeve where the molten metal charge is poured into the shot sleeve for introduction into the die cavity by movement of the plunger as described hereabove.
Use of the melt transport ladle for introducing successive molten metal charges to the shot sleeve is time consuming and requires continual movement of the melt supply ladle between the melting furnace and the shot sleeve of the die casting machine in order to maintain production. Moreover, the temperature of the molten metal charge can drop considerably during transport from the furnace to the shot sleeve. As a result, the melt temperature in the melting furnace is maintained higher than would otherwise be required. Higher melt temperature will aggravate thermal shock to the shot sleeve, plunger, and die members when the molten charge is supplied thereto.
Furthermore, during ladle transport from the melting furnace to the shot sleeve, the molten metal is exposed to ambient air and foreign matter in the air. As a result, the levels of oxide and other inclusions, dross, and sludge in the melt in the ladle can be increased and adversely affect the quality of the die casting produced therefrom.
It is an object of the invention to provide improved melt pumping apparatus having a pump casing or housing, a piston, and melt inlet/outlet flow control valves submersible in the melt in a melt-holding vessel and useful for supplying a controlled amount of melt from the vessel to a melt casting machine, whereby the aforementioned disadvantageous associated with use of the aforementioned melt transport ladle that continually moves between the melting furnace and the metal casting machine are eliminated.
It is another object of the invention to provide improved melt pumping apparatus having pump components comprising melt-resistant ceramic material submersible in a melt-holding vessel and operable over long time periods to supply a controlled amount of melt to a melt casting machine.
It is still another object of the invention to provide melt casting apparatus wherein a controlled amount of melt is pumped directly from a melt-holding vessel to a melt casting machine by a melt pumping apparatus via a melt supply conduit.